Cell adhesions, cell junctions and extracellular structures Flashcards
Epithelium
sheets of cells that are
polarized, with discrete functional
domains at opposite ends (apical and
basal) of the cells.
Connective tissue
more loosely
organized, in which cells are attached
to each other, a rigid scaffold, or both
Cell-Cell Junctions
Specialized structures where
two cells come together are
called cell-cell junctions
Type of animal cell junctions
- Adhesive junctions
- Tight junctions
- Gap junctions
plant junctions
Plant cells have special structures
called plasmodesmata
cell table
Adhesive Junction
Link adjoining cells
* Adhesion proteins are key
* Some need a linker protein
* Cadherins
* Are dynamic
Types of adhesive junctions interactions
Homophilic interactions: same
* Heterophilic interactions: different
Cadherin characterisation
“Repeats” in their extracellular domain
➢ A transmembrane domain.
➢ Varying cytosolic ends.
E-cadherins
E-cadherins are found on epithelial cells
P-cadherins
P-cadherins in placenta (and other tissues)
Cadherin function
- The amount and type of cadherins on cell surfaces help
segregate cells into specific tissues. - Cadherin expression is essential for organization of cells during
development
Desmosomes
Provide a tissue with structural
integrity
* The desmosomal cadherins are
called desmocollins and
desmogleins.
* Linker protein = planktoglobin
cell-cell adhesions for cellular events
- Lectins
- Cell adhesion molecules
(CAMs) - Selectins – e.g. Leukocyte
adhesion during
inflammation.
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Tight Junctions
Seal the gap between
adjacent epithelial
cells
Tight junction protein types
Proteins include:
➢occludin
➢junctional
adhesion
molecules (JAMs)
➢claudins
Gap Junctions
- Allow direct electrical & chemical communication
- Connexons form 3 nm wide channels
ECM types
bone
Cartlidge
Connective tissue
Bone
Rigid ECM with few
interspersed cells
Cartlidge
More flexible than bone
Connective tissue
Gelatinous with
interspersed fibroblasts
Three Classes of ECM Molecules
- Structural proteins → collagens & elastins
- Protein-polysaccharide complexes → proteoglycans
- Adhesive glycoproteins →fibronectins & lamins
collagen
Elastin
Proteoglycans
glycoproteins where many glycosaminoglycans
(GAGs) attach to a single protein
Adhesive Glycoproteins
Adhesive Glycoproteins Anchor Cells to the
Extracellular Matrix
* Direct links between the ECM and the plasma membrane are
reinforced by a family of adhesive glycoproteins
* They have multiple domains to bind molecules in the ECM and
receptors on membranes
* Laminins and fibronectins
Fibronectins
- Glycoproteins in the ECM
- Many isoforms exist
- 2 subunits connected by SS
bonds - Rod-like domains bind specific
ECM molecules / cell surface
receptors
Laminins
Glycoprotein
* Bind cells to the basal lamina
Basil lamina
- Basil lamina = structural support & barrier
- Cells can alter properties of the basil
lamina - Matrix metalloproteinases degrade local
ECM at the basil lamina
Laminin structure
Integrins
- Cell surface receptors → bind ECM
constituents - Transmembrane proteins with α&β domain
- Many isoforms:
- α5β1 binds fibronectin
- α6β1 binds laminin
Hemidesmosomes
- In epithelial cells
- α6β4 integrin
- Attach to laminin in the basil lamina; to keratin in the cytoskeleton
Anchorage-dependant growth
Anchorage independent growth
paracellular transport and barrier
tight junction structure
Leukocyte rolling
Lectins allow leukocytes to roll on top of epithelial cells instead of just free-floating by being passed from one cell to another
-selectin expression is increased by inflation
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Focal adhesions
